The above-cited automatic machines comprise machines which have an unwinding station, from which the strip is guided to form a first loop buffer and then is fed towards a printing station, where at least a side of the strip is printed upon.
Normally the printing is organised according to a traditional page-setting with a standard format, for example A4 type, so that there will be a plurality of pages flanked according to the width of the strip, for example two or three, and a corresponding number of lines of pages along the development of the strip.
There is for this reason a need to separate each longitudinal line of pages from the ones flanked thereto and, thereafter, to separate the consecutive pages of each line, such as to perform subsequent operations, such as formations of collected stacks and packing thereof into envelopes.
For this reason, downstream of the printing station a first station is provided for longitudinal cutting, in which the longitudinal separation of the lines is performed, possibly together with a trimming operation; the organs of the first station operate with a continuous advancement of the strip.
The flanked strips in outlet are first guided to form relative second loop buffers and are then subjected to progressive deviation, in transversal directions, such that one is brought to above another, before entering, in this configuration, a second station for transversal cutting, provided further downstream.
The formation of the second loop buffers is made necessary both in order to unload the longitudinal tension from the lines before operating the lateral deviation on them, and also because the organs of the second cutting station operate with a step-advancement.
The lateral deviation of the lines, necessary for their superposing, inevitably generates asymmetric transversal tension in the paper (which is not extensible) that tend to cause the strips to swerve, which not uncommonly results in their tearing, with all the drawbacks connected to resetting the line.
The above drawback is more likely to occur when using light paper reels, with weight of 60 gr/m2 instead of the traditional 80 gr/m2.
The intermittent advancing of the strips can be differentiated according to the storing program between the pages of the various lines; if the stack to be formed is not an exact multiple of the number of lines present in the strip, one or the other line in inlet to the cutting station has to be selectively halted, possibly both in turn, such that only the pages destined thereto reach the store where the stack is formed, downstream of the cutters.
This situation can increase the stress forces on the strips and increase the possibility of tearing occurring.
The above-described conditions impose rather low working speeds, which negatively impact on production costs.